It is currently possible to transmit audiovisual programs in digital form via broadcasting networks of the microwave (herzian), cable, satellite type, etc. or via telecommunication networks of the DSL type (Digital Subscriber Line) or BLA type of (Local Radio Loop) or via DAB networks (Digital Audio Broadcasting) as well as via any wireless telecommunication network of the GSM (Global System for Mobile), GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunication System), Bluetooth, WiFi types, etc. Moreover, to avoid the pirating of works broadcast in this manner these works are frequently encrypted or scrambled by various known means.
U.S. Pat. No. 6,295,361 discloses a method and device that permit a key management node to decide the process for changing the group key of certain nodes in a multicasting group with the aid of an indicator inserted into a multicast packet. The management node decides how to insert the indicator and which nodes are concerned. The new key is then sent and when all the nodes of the group have received their key, the management node sends an indicator or also a date from which all the members of the group are authorized to use the new keys. Thus, a method for managing the multicast session with the aid of dynamic changing of the group keys is disclosed. The same key is attributed to all the members of the same group with the aid of which the data is decrypted. However, the protection used is the encryption and all the data initially present in the audiovisual stream remain in the protected stream. Consequently, U.S. Pat. No. '361 does not resolve the problem of high security and personalization.
WO 02/11356 A2 discloses a method for managing keys between the client and the server in a multicast environment. The method is based on establishing a secure channel between the server and the client using an SSL protocol (Secure Socket Layer) or TLS (Transport Layer Security) with certain modifications of the order of exchanging of messages to be able to generate a management key and send the key to the client via the secure channel, from which key the client generates a future key for the session with the server. The clients of one and the same multicasting group use the same management key for generating a session key during the communication session. WO '356 does not correspond to the criteria for the secure transport of audiovisual data and the data, even the encrypted data, is integrally present in the protected data stream.